1. Field of the Invention
The present invention relates to a smoke detector capable of optically detecting smoke, contaminants, and the like floating in the air.
2. Description of the Related Art
Hitherto, there has been used a smoke detector for detecting smoke so as to prevent and extinguish a fire, or for detecting contaminants (dust or the like) so as to preserve an environment in a semiconductor manufacturing plant, a food factory, or the like (so-called clean room or the like).
Among various smoke detectors, there is an optical smoke detector for optically detecting smoke and contaminants contained in the air (hereinafter referred to as “smoke or the like”).
The optical smoke detector can detect smoke or the like in such a manner that a light receiving section receives scattered light generated in a smoke detecting section when light emitted from a light emitting section is scattered due to particles of the smoke or the like.
The optical smoke detector is provided with an aperture through which light emitted from the light emitting section passes in order to control the size of the passing region of the light emitted from the light emitting section or prevent generation of stray light (diffracted light). Generally, this aperture is formed integrally with a main body of a case of the smoke detector (for example, see paragraph 0014 and FIGS. 1 to 3, etc. of Japanese Patent Application Laid-open No. Hei 11-248629).
In the smoke detector of this type, it is preferred that a thin aperture that has a small contact area with respect to the passing light be used in terms of preventing generation of diffracted light. Therefore, it is conceivable to reduce the thickness of the aperture.
When the thickness of the aperture is reduced, the strength may become insufficient when the aperture is merely thinned. Therefore, although integral formation of the aperture and the main body becomes impossible, it is conceivable to use another hard material such as an iron plate as an aperture member.
Note that, in the case of the smoke detector of this type, an LED or a laser may be used as a light source of the light emitting section (for example, see paragraph 0012 of Japanese Patent Application Laid-open No. Hei 11-248629). The directionality of light is higher when the laser is used than when the LED is used. In view of preventing generation of diffracted light, it can be said that a greater advantage can be obtained by thinning the aperture.
However, when another material such as an iron plate is used as the aperture member, an operation of mounting the aperture member to the main body is necessary. At this time, an operation of locating the center position of a light passage opening of the aperture member on an optical axis of the light emitting section is necessary.
Further, in order to form the aperture member from the iron plate or the like, piercing is performed to form the light passage opening. Depending on the process method thereof, however, burrs or the like may remain on an opening edge portion of the light passage opening on one surface side in a front-back direction. When the aperture member is mounted to the main body while orienting the surface side on which burrs or the like are liable to remain due to the process toward the light emitting section, if the burrs or the like are left, the burrs or the like may cause generation of diffracted light.
That is, in the case where another material such as an iron plate is used as the aperture member, when the aperture member is assembled to the main body, it is necessary to not only locate the center position of the light passage opening of the aperture member on the optical axis, but also appropriately orient the aperture member in a desired normal direction in the front-back direction (orientation in which, when the surface side in which the burrs or the like are less liable to remain is the front surface side and the surface side in which the burrs or the like are liable to remain is the back surface side, the front surface side is oriented toward the light emitting section, and the back surface side is not directed toward the light emitting section).